Timing by Degrees

bobber · Post by **bobber** » Wed Mar 03, 2010 1:43 pm

Hi, the manuals I have for the G5 Lightweight state that Ignition Timing should be set fully advanced at 1/4 inch BTDC, using the dip stick method through the plug hole. Does anyone know the BTDC setting in degrees when using a timing disc on the cranckshaft?
Regards, Andy.

Don Madden · Post by **Don Madden** » Wed Mar 03, 2010 4:13 pm

Why, unless you want to use a strobe? The combustion process is only indirectly related to crankshaft angle but is directly related to the piston position. If you wish to use a strobe, the it will show the dynamics better but the piston position is still better to establish the reference marks. Cheers, Don.

bobber · Post by **bobber** » Wed Mar 03, 2010 4:34 pm

Don, thanks for the advice; my reason for enquiring after the timing disc option is because I'm fitting electronic ignition and was under the impression (wrongly perhaps?) that it will provide greater accuracy - necessary for electronic ignition? What's your opinion?
Regards, Andy

lawrence · Post by **lawrence** » Wed Mar 03, 2010 7:56 pm

quote:
necessary for electronic ignition?

Even with EI the rod down the plughole is better. I tried both methods on my twin and the bike ran better with the standard method of ignition setting.

Don't use a pencil..............

Ludwig · Post by **Ludwig** » Thu Mar 04, 2010 10:52 am

1/4" BTD at 85.5mm strocke results in an angle of 28 degrees - assuming a typical crank-ratio
(I don't know the con rod length, but the influence is very small, less then +- 0.5 degrees).
Regards Ludwig

Stan Palmer · Post by **Stan Palmer** » Thu Mar 04, 2010 3:34 pm

The various manuals for the '53 350 variously state the measured BTD as 3/8, 7/16 or 1/2", but the only angle figure I have seen is 37.
So I built a spreadsheet to calculate mm and degrees (probably the same as Ludwigs as the result for 85.5 stroke is the same as he said). 37 degrees corresponds to the 1/2" measurement for the 93mm stroke 350 by the way.
If anybody wants a live copy of the spreadsheet send me a PM with email number as the forum email doesn't allow attachments. You have to know how to use Goalseek.
Stan

bobber · Post by **bobber** » Thu Mar 04, 2010 10:59 pm

Dear all, Apologies for the delay in responding - work got in the way!! Many thanks for all the advice; it's been very helpful and much appreciated. Stan - I've responded to your e-mail.

Regards,

Andy.

aobp11 · Post by **aobp11** » Fri Mar 05, 2010 10:26 pm

Stan, not very important but published degrees for 350 vary also. One 1954 instruction book says 35 1/2 at 7/16" but another one, also 1954, says 37 at the same 7/16". For 1955: 39 at 1/2". The published figure for 1/2" corresponds to my calculations (38.8) while I get 36.1 at 7/16".
Albert